Passive margins in accreting Archaean archipelagos signal continental stability promoting early atmospheric oxygen rise

Significant changes in tectonic style and climate occurred from the late Archaean to early Proterozoic when continental growth and emergence provided opportunities for photosynthetic life to proliferate by the initiation of the Great Oxidation Event (GOE). In this study, we report a Neoarchaean passive-margin-type sequence (2560–2500 million years ago) from the Precambrian basement of China that formed in an accretionary orogen. Tectonostratigraphic and detrital zircon analysis reveal that thermal subsidence on the backside of a recently amalgamated oceanic archipelago created a quiet, shallow water environment, marked by deposition of carbonates, shales, and shallow water sediments, likely hosts to early photosynthetic microbes. Distinct from the traditional understanding of passive margins generated by continental rifting, post-collisional subsidence of archipelago margins represents a novel stable niche, signalling initial continental maturity and foreshadowing great changes at the Archaean-Proterozoic boundary.


Line 29 represents
Line 29 delete "environmental"; it is either redundant or even wrong (niches are ecological phenomena) Line 31 Aren't "initial" and "proto"(continental) kind of redundant?
Line 32 Archaean-Prot boundary most certainly isn't "early Earth", which is typically applied to Hadean and the earliest Archean eras only. Delete and save some words for better abstract.
Line 34-37 Quite a word salad for a first sentence! Do you really need to lead with the contentious onset of PT? Largly irrelevant by late Neoarchean-when likely everyone in the world, with few or one exception, already expects PT would have been operational. Why not just jump into the contentious GOE and the even more contentious pre -GOE "whiffs" of oxygen Line 38 submerged Lines 34-40 short first paragraph (especially if you delete the essentially irrelevant onset of PT debate; previous comment); consider moving Lines 41-45 up to paragraph one.
Line 45 "In this study, we report…" (NC formatting guidelines) Line 45 passive-margin type shallow water sequence (these hyphenation corrections will not be repeated but should be corrected throughout)   This paper reports a suspicious Neoarchean passive margin-type sequence from the North China craton. Tectonostratigraphic and detrital zircon analyses are approached to decipher its nature. It is concluded that this unit was sitting on the open-oceanic backside of an amalgamating arc terrane in a shallow-water environment due to local thermal subsidence. If this is approved, it represents a stable environment that is distinct from the typical passive margins, but might be a specific environment signaling initial protocontinental maturity. This environment might provide a new opportunity for oxygenic lift prior to the Great Oxidation Event. This study is innovative -not only declaring an unique sequence at the initiation of continental maturity in the Neoarchean, but also explaining the possible mechanism of subsidence of early continent to create shallow-water environment to be capable of early oxygenic life. My major concern is the age of the key tectonostratigraphy in the paper. Although it has not been clarified directly in the paper (it should have had), it is quite clear that the key sequence includes the Gantaohe Group based on the geological map ( Figure 1) and the description of its four units. There are many previous local and international publications for this group (e.g., Liu et al., 2012;Du et al., 2016). It is well-known that it is the Paleoproterozoic in age since its definition in 1960s (for example, there is an age of ~2.1 Ga for volcanics: Du et al., 2016). All these previous data on the group should be at least reorganized and evaluated. Another major concern is the interpretation on the tectonic environment of the sequence. It is quite depending on the author's own model on the tectonic evolution of the region, as well as their interpretation on the age of the Gantaohe Group (see above). Based on the sedimentary facies of the group, as well as the chemical and geochronological data already reported, it has been proposed that the Gantaohe Group was developed on the continental crust, either in an intra-continental rifting environment (e.g., Du et al., 2016 and many other researches) or a back-continental arc environment (e.g., Liu et al., 2012). In addition, both the mechanism for the subsidence of the so-called 'Neoarchean' passive marginal basin and its link with the Great Oxidation Event are not adequately supported by the data provided in the paper (hardly proved but just stated). Is there any sign of thermal subsidence of the region? Is there any fossil or tracer to prove the nourish of oxygenitic life in the sequence? With the above concerns in mind, I think this innovative work is rather inadequate at this stage. I would be happy to see more evidence to depict itif it has been proved, it would have provided a totally new concept to the research field, which with no doubt would be revolutionary.
Abstract: Line 19-21: this statement on the significance of 'the emergence of stable shallow-water continental platforms' is rather arbitrary.
Line 26: how do you know it was on 'the open-ocean back-side'? If it was on the openocean back-side, we won't call it a 'passive margin'?
Line 28: it is likely that there was no indication of 'microbes' in the stratigraphy (e.g., there was even no stromatolite in the carbonates).
Line 48: 'this data' should read 'these data' or 'the dataset'.
Line 53-59: many geologists suggested that the eastern craton and western craton were collided at 1.9-1.8 Ga, rather than 2.9-2.5 Ga. Please at least mention this option.
Line 60-63 '… causing deformation and metamorphism between 2.7-2.55 Ga to form protocontinental nucleii…'however, there are hardly metamorphism ages of 2.7-2.55 Ga in the North China craton. Actually, the widespread metamorphism in this craton was happened most likely after 2.55 Ga. BTW, 'nucleii' should read 'nuclei'?
Line 72-80: the regional geology should start with the units defined by local workers, and then you may specify your tectonic interpretation for each unit. Line 146-151: why this metabasalt-featured unit allochthonous slice rather than a part of the stratigraphy? The whole sequence was well-known as the Gantaohe Group in the literature. Although it has undergone stronger deformation in the middle of the Zanhuang region, it shows quite consistent sequences with those west to the region will less deformation. It is well-known to be a Paleoproterozoic intracontinental sequence.
Line 149: It should be noticed that the Archean basement in the COB has varied ages from 2700-2500 Ma.
Line 152-155: The statement here is arbitrary.
Line 157-159: Observation is needed to show an overthrust allochthonous unit. A tectonic/fault contact does not guarantee an allochthonous origin.
Lines 165-166: Sure thing. The basement is older than 2.5 Ga; while the strata was middle Paleoproterozoic in age.
Line 169-176: yes, there was probably an episode of metamorphism at the late Archean, but the major episode was the late Paleoproterozoic.
Line 182-186: Again, it is reasonable that the deformation of the basement and the Gantaohe Group (unit 1-4) is different.
Line 190-247: sorry I did not read it in quite detail. It is really hard to follow as the major deformation here, or at least the deformation as revealed by Ar-Ar ages is the late Paleoproterozoic. Without distinguishing the Archean and Paleoproterozoic episodes of deformation, it is really hard to evaluate the description.
Line 266-269: the error of these ages are quite large, over 20 Ma or 30 Ma. There are no obvious differences between these age groups to discriminate their provenances.
Line 270-286: I admit that there could be a successive thermal/igneous event in the region during the Late Archean; then how can you distinguish ages between domains with lead loss and domains not, especially considering their large errors of singular ages.
Line 287-335: all these analyses and interpretation is based on the assumption that the sequence was the late Archean in (depositional) age. But that was not the case, the volcanics (metabasalts) and other rocks show clear evidence that the rocks are middle Paleoproterozoic in age (e.g., Du et al. Line 321-325: it analyzed the age of a crosscutting metamorphosed mafic dyke, which gives a U-Pb zircon age of 2507 Ma. I highly doubts whether this is an age of crystallization or an age from inherited zircon grains, and hence, it is inadequately proved that this ~2507 Ma age is a key to constrain the deposition age of the tectonostratigraphy.
Line 338-340: But the whole basement was not exhumed until the Late Paleoproterozoic; how can it be the exposed coast in the Archean.
Lines 358-361: 'Thus, the results strongly suggest the autochthonous passive margin sequence was deposited concurrently with accretion of multiple arcs, with intervening oceans of different ages, in an accretionary orogen, similar in style to the Altaids of central Asia'. All the ages provided in the paper are within-error quite similar, and nothing of the kind can be supported.

Response to Reviewer #1
Reviewer #1 (Remarks to the Author): Thanks for the opportunity to review this very interesting manuscript, the authors present good field observations and nice data on the Archaean North China Craton and the Great Oxidation Event with the global vision. The manuscript should be of general interest to a wide audience. It is well written and the figures are all extremely well-done and convey the message. I recommend publication after minor revision, with a few suggestions below, my concerns mainly include: (1) this manuscript showed a nice field observation in the Zanhuang mélange of the North China craton, but I would suggest the authors should improve the field interpretations a little bit, such as Figure 4, the authors might miss some important information among the blocks, and also some different foliations/boundaries; (2) I didn't see the carbonate in the field photos, maybe, the authors forget to identify them, however, it's such a really nice parametamorphic rock association in the NeoArchaean Zanhuang mélange; (3) In the Figure 1D, they should be foliations? but they were identified as like the bedding. Scales are need in the geological maps and all filed photos. I don't comment on the tectonic model discussion, it looks reasonable to me. This is an excellent idea with field data to support it about Archaean geology with implications for the leadup to the GOE. The accretion of ocean arc archipelagos is likely how many cratons formed-explaining nicely the granite-greenstone architecture of most Archaean cratons. The authors present the clever idea that the passive margins of Archaean archipelagos that accreted to form protocontinents would have, upon continental stabilization, subsided and created shallow water ecospace in which photosynthetic bacteria could have thrived and therefore eventually caused the tipping point of the GOE. Although their locality, North China craton, is just one, the authors are correct to point out that it is the *cumulative* effect of the cratons stabilizing globally that would have led to this increased ecospace over time, with later-forming cratons like North China being the proverbial "straw that broke the camel's back". The work is detailed and robust and the idea is compelling and fitting for publication in a general journal like Nature Communications. Although my comments below may seems critical, they are made only in an effort to improve an already strong and provocative paper. I would recommend MINOR REVISIONS.
REPLY: Thank you for the positive comments! Major comments (1) The pre-GOE oases, or pre-GOE "whiffs" of oxygen should not be taken as fact and the authors must admit somewhere that there is uncertainty about their existence. In fact, they are quite contentious and potentially dubious post depositional diagenetic artifacts (Slotznick et al., 2022). There is also depositional modeling inspired by the Archaean presence of redox-sensitive detrital grains of pyrite and uraninite (easily weatherable if free oxygen is available anywhere in the atmosphere) that casts theoretical doubt on the existence of pre-GOE "whiffs" of oxygen, suggesting the rise of oxygen must be younger than 2415 Ma (Johnson et al., 2014). I would therefore recommend the authors instead focus on the "leadup" or the "prelude" to the GOE. 2.5 Ga is not the start of the GOE. Some think the GOE was late as 2.33 Ga (Luo et al., 2016). Even if as old as <2415 Ma (Gumsley et al., 2017), the authors' archipelago subsiding backsides are still not a "coincidence" with the GOE, but a prelude or leadup to it. Perhaps the delay can be explained in terms of subsidence creating sufficient accommodation space that shallow platformal shelves covered enough areal extent to finally promote the full-fledged GOE. Furthermore, the more arcs that protocontinents accreted, the more continents would stabilize and such larger and higher continents would shed more sediment, making it more likely to form broad continental shelves to provide the ideal shallow water ecospace for photosynthetic bacteria. Also, it could be mentioned that sourcing rock-derived phosphorous as nutrients (which would be rich in apatite in basalts of ocean arcs) is a prerequisite for the GOE (Cox et al., 2018). Whereas evidence of photosynthesis may substantially pre-date the GOE (Nutman et al., 2016), nutrients were likely the rate-limiting reactant, which the authors' model can nicely explain.

REPLY:
We appreciate the critical and insightful comments of reviewer Ross Mitchell. You made good points which we largely agree with, and have modified the text as suggested throughout the text, as shown by the highlighted sections. Indeed, the notion of oxygen whiffs is contentious depending on the methods used to detect oxygen level, and the common agreement made by previous research, and our article as well, is merely that the oxygen oasis would remain in limited areas (as oases) if they do exist. The thing is, GOE would only be recorded when the concentration of oxygen level in the global atmosphere reaches to a threshold that allows oxygen to be widely involved in chemical reactions, which will make the timing of defined GOE delayed to the first emergence of oxygen oasis. The 2.4 to 2.3 Ga initiation time of the GOE 2, 3, 4 does not conflict with our presumption, and is in agreement to the numerical model of oxygen level we referred to in the article 5 . The work here is meant to explain the transition between pre 2.5 Ga anoxic Earth and the 2.3 Ga oxidized planet. The point we try to make through the article is to provide a tectonic or geodynamic model linked to these oxygen oases and to imply the connection between continents formed by arc accretion and the global atmospheric changes by regional oxygen whiff accumulation. The general idea is that, by amalgamating arcs to form continents at around 2.5 Ga, the subsidence of protocontinent margins would contribute to oxygen formation, and as more continents became stabilized, the oxygen level would thus rise to the level and would trigger the GOE.
(2) In the profile description, it seems the island arc (graywacke) and backside sediments (calc-silicate) are conformably contacted? If so, why do the carbonates necessarily occur in a backside setting? These sediments can simply be part of the arc (arcs may have hiatus). Some Phanerozoic intra-oceanic island arcs have volcaniclastic rocks interbedded with the carbonate. If the island arc is in fault contact with the backside sediments, are these backside sediments comparable with the continental passive margin sediments? If they are, it means the island arc is in fault contact with both sides of the sediments. Then the simplest way to understand the arc-continent collision process is that the arc might have been thrust onto the continent (like the Macquarie Arc in SE Australia).\ REPLY: Thanks for the insightful comments. We would like to make it clear that the graywacke and underlying sandstone are interpreted to be products of immature continental margin costal sedimentation. And yes, they are in conformable relationship to the overlying calc-silicious rock. It is true that an intra-arc environment is capable of producing carbonate deposition, as in Taiwan, and the Banda Arc, etc. The differences are that in an intra-arc setting, the carbonate is interbedded within graywacke, which indicates back and forth regression and transgression settings or turbulent conditions. In our case, the graywacke does not reappear upon the carbonate sequence and there is a significant transition to a quiet and stable platform setting with details described in the text. It might be argued that the later deformation truncated the sequence, preventing the preservation of the later graywacke. But the sedimentation age constrained by the MDA in the carbonate-mudstone unit (ca. 2510 Ma) is so close to the collisional event (~2510-2500 Ma) that would leave fewer possibilities for further sedimentation. This is our evidence to support that the carbonate-mudstone represents the end of this sequence. In summary, our sequence indicates a transgressive and stable platformal environment, distinct from the regressive-transgressive and unstable intra-arc setting.
After that, at 2510-2500, the outboard arc was thrust upon the continent forming to the east, so our model is indeed consistent with your suggestions.
(3) Arc-continent collision process might be the direct contribution to any variations of the environment in this case (?). You have constantly new passive margins replacing the old ones. There is nearly no net increase of passive margin only from this process (assuming the length isn't changing as it's not discussed here). The continent is growing, but the passive margins are just constantly being replaced. The direct observations from the evidence shown in this paper are 1) arc-continent collision processes resulted in 2) continental growth/addition of carbonate. Thus, it would be clearer to state that arccontinent collision process is the key (?). The proposal of Phanerozoic arc-continent collisions in the tropics set Earth's climate state might be worth to be referred (Macdonald, Francis A., et al. Science 364.6436 (2019)).

REPLY:
Thanks for pointing out this statement. Yes, you are right. The key is the continuous arc collision and amalgamation. The passive margin in arc-accretion setting is the result of arc amalgamation forming protocontinents, and the link between arcaccretion (tectonic) and the possible atmospheric change (sedimentation). Our study is the direct field evidence to indicate the influence of tectonic style to the planet's atmospheric changes.

Minor comments
By my count the current title is two words over the 15-word NC limit. I might suggest: Passive margins in accreting Archaean archipelagos signals continental stability and creation of pre-GOE oxygen oases (I would avoid the word "emergence" for meaning "appearance of" or "rise of" passive margins given that the paper also discusses continental emergence, i.e., above sea level.) Archaean should use UK spelling for this journal REPLY: Thank you for pointing it out. We have revised the spelling throughout, and fixed the title to fit the word limit, and limit our use of the word emergence to refer to only emergence of continents above sea level to avoid confusion.
Abstract is quite good, but could be better. Some words to delete are suggested that may allow for a better re-write REPLY: Done. Thanks. Line 19 see comment about not using "emergence" unless continental emergence REPLY:

Response to Reviewer #3
Reviewer #3 (Remarks to the Author): This paper reports a suspicious NeoArchaean passive margin-type sequence from the North China craton. Tectonostratigraphic and detrital zircon analyses are approached to decipher its nature. It is concluded that this unit was sitting on the open-oceanic back-side of an amalgamating arc terrane in a shallow-water environment due to local thermal subsidence. If this is approved, it represents a stable environment that is distinct from the typical passive margins, but might be a specific environment signaling initial protocontinental maturity. This environment might provide a new opportunity for oxygenic lift prior to the Great Oxidation Event. This study is innovative -not only declaring an unique sequence at the initiation of continental maturity in the NeoArchaean, but also explaining the possible mechanism of subsidence of early continent to create shallowwater environment to be capable of early oxygenic life.
Thank you for the summary. We apply field mapping, including base maps from the Geological Survey, tectonostragphic analysis, structural analysis, detrital zircon analysis, and analysis of the U-Pb and Pb-Pb ages of cross-cutting units, and the ages of late NeoArchaean metamorphism to make our interpretations of this Archaean sequence. My major concern is the age of the key tectonostratigraphy in the paper. Although it has not been clarified directly in the paper (it should have had), it is quite clear that the key sequence includes the Gantaohe Group based on the geological map ( Figure 1) and the description of its four units. There are many previous local and international publications for this group (e.g., Liu et al., 2012; Du et al., 2016). It is well-known that it is the Paleoproterozoic in age since its definition in 1960s (for example, there is an age of ~2.1 Ga for volcanics: Du et al., 2016). All these previous data on the group should be at least reorganized and evaluated.

REPLY:
Thank you for your critical comment to help us clear up the possible confusion from future readers. We should have made it clarified in the previous submission, that we are dealing with the Archaean sequence, not the Proterozoic cover (Gantaohe Group).
According to the geological map and previous research work cited in both this work and the comments, the reported rock has well-constrained Archaean age and is distinguishable to the Proterozoic Gantaohe Group.
1) The Gantaohe Group is located about > 28 km northwest of our sequence, and rests unconformably over the Archaean Western Zanhuang Domain (WZD, see Fig.1b) in our article. It is in no way same to the strongly deformed sequence reported in the manuscript that is normally considered as the 'Archaean basement' in research related to Gantaohe Group.
2) We are working on the Archaean basement, and our robust geochronology studied on both the sedimentary units, and the cross-cutting igneous units, indicate unequivocal Archaean age. These rocks were originally mapped as the Neoarchean Fangjiapu Formation in the Zanhuang Group (or Tuanpokou Formation in Fuping Group), see ref.
23, 24 in the main text.
3) Although the rock assemblage is broadly similar, the sequence of Gantaohe Group is related to a Proterozoic rifting event according to previous research, 400 million years younger than the arc-continent collisional event correlated to this sequence (line 245-254).
Although the relationships are certain, we would like to apologize to the reviewer for not making that clear in the initial submission. In order to clarify the misunderstanding, we have revised our Figure 1b, to show the location of the Gantaohe Group in relationship to the rocks we described, and have added a new couple of sentences, stating the official formational rank names of these rocks, and refer to the 1:50,000 scale geological maps. As stated in the text, we used these geological survey maps of the Archaean basement, as base maps for our own maps and defined a stratosection, based on their previous work, as stated on lines 83-89, and 92-99. The statement is: (Fig. 1b) showing that major deformation in the Zanhuang massif was over by that time.

These rocks were originally mapped as the Fangjiapu Formation in the Zanhuang Group (or Tuanpokou Formation in Fuping Group) 23,24 , but in following sections, we use a lithostructural nomenclature based on our new results. Parts of the Western Zanhuang Domain are unconformably overlain by flat-lying sedimentary and volcanic rocks of the 2.1 Ga Gantaohe Group 22,23
Another major concern is the interpretation on the tectonic environment of the sequence. It is quite depending on the author's own model on the tectonic evolution of the region, as well as their interpretation on the age of the Gantaohe Group (see above). Based on the sedimentary facies of the group, as well as the chemical and geochronological data already reported, it has been proposed that the Gantaohe Group was developed on the continental crust, either in an intra-continental rifting environment (e.g., Du et al., 2016 and many other researches) or a back-continental arc environment (e.g., Liu et al., 2012).

REPLY:
The Gantaohe Group relates to a much later event later than the 2.5 Ga arccontinent collision 1, 6 . We agree with the mechanism proposed by previous research on the genesis of Gantaohe Group. But this paper is not about the Gantaohe Group, it is about the underlying late Archaean basement.
In addition, both the mechanism for the subsidence of the so-called 'NeoArchaean' passive marginal basin and its link with the Great Oxidation Event are not adequately supported by the data provided in the paper (hardly proved but just stated). Is there any sign of thermal subsidence of the region? Is there any fossil or tracer to prove the nourish of oxygenitic life in the sequence?

REPLY:
Our age data on the NeoArchaean age of this sequence are robust, supported by our detrital zircons, Archaean metamorphic rims on zircons, and crystallization age of cross-cutting late Archaean igneous rocks.
Like many other Archaean metasedimentary rock, the sequence is highly deformed and metamorphosed, so fossils and tracers are difficult to be preserved in this condition. However, by considering the genesis of this thick carbonate sequence, we can decipher the presence of oxygen generating microorganisms. The transgressive nature of the sequence indicates a subsidence of the protocontinental margin.
Our work here, as well as that of the Geological Survey of Hebei Province, for more than two decades, indeed provides a solid framework for our interpretation, and is meant to provide a tectonic or geodynamic model linked to these oxygen oases and to imply the connection between continents formed by arc accretion and the global atmospheric changes by regional oxygen whiff accumulation at the same time frame. The general idea is that, by amalgamating arcs to form continents at around 2.5 Ga, the contemporary subsidence of the protocontinent margins would form environmental habitats suitable for organisms to thrive, and contribute to oxygen formation, and as more continents get to stabilized, the oxygen level would thus rise to the level and would trigger the GOE.
With the above concerns in mind, I think this innovative work is rather inadequate at this stage. I would be happy to see more evidence to depict itif it has been proved, it would have provided a totally new concept to the research field, which with no doubt would be revolutionary.

REPLY:
Thank you for the comments. The question you raised are addressed in detail below, but we need to clarify again, that we are not describing the Gantaohe Group in this work, we are describing and interpreting the Archaean basement. We do not cite these papers, since they are about the Proterozoic Gantaohe Group, and our work is about the Archaean basement, not the Gantaohe Group. These papers do NOT include our described sequence as part of the Gantaohe Group. In fact, the first paper argues that since the Gantaohe Group is virtually undeformed, it was deposited after any collisions, which is quite consistent with our work.
Abstract: Line 19-21: this statement on the significance of 'the emergence of stable shallow-water continental platforms' is rather arbitrary.

REPLY:
Thank you for pointing it out. We have corrected it to be more appropriate now.

REPLY:
Thank you for the question. The tectonic setting is based on our regional tectonic synthesis. Our demonstration on the passive margin can be referred to lines 91-160, and 343-349. We note that our example, and some of the others are not "traditional Wilson Cycle" passive margins, where a previously existing large continent rifts, thermally subsides, then has a passive margin developed on it. This is an accretionary orogen, where the transgressive shallow water sequence developed on the back arc side of very recently amalgamated arcs. Related revised text is on lines 354-369, and 371-378.
Line 28: it is likely that there was no indication of 'microbes' in the stratigraphy (e.g., there was even no stromatolite in the carbonates).
REPLY: Good question. Considering the highly deformed and metamorphized nature of this rock suite, finely laminated stromatolites are unlikely to be preserved. The deformation of the carbonate-mudstone unit is indicated in Fig. 7.
Line 48: 'this data' should read 'these data' or 'the dataset'.

REPLY: Corrected.
Line 53-59: many geologists suggested that the eastern craton and western craton were collided at 1.9-1.8 Ga, rather than 2.9-2.5 Ga. Please at least mention this option.

REPLY:
Thank you for raising this question. The 1.9-1.8 Ga collision has been proven incorrect by many papers in various journals, including in this journal 7 . The proposal of a 1.9 or 1.8 collision with the suture in this zone is clearly inconsistent with basic geological facts, for instance, the 2.1 Ga Gantaohe Group is virtually undeformed, and sitting on the site of the proposed 1.8 Ga suture in those studies, proving that there was no 1.8 Ga collision in this area (for instance, see the paper by Du et al., above, that you ask us to cite).
We, and others, discuss this debate in many papers. However, it is not the subject of this paper. Here, we are describing the 2.56-2.50 Ga shallow water sedimentary sequence, and its involvement in a 2.50 Ga arc continent collision, which is well established. We, nevertheless, have addressed the 1.8 metamorphism overprinting in our work very clearly in Supplementary Discussion 2, lines 138-144. The 1.8 Ga metamorphic event is recorded nearly everywhere in the craton, and not related to a specific event in this location.
Further, we are not saying the Eastern and Western Blocks collided at 2.5 Ga as a single event. The eastern Block likely formed by arc amalgamation by 2560 Ma, then the next arc of the Central Belt collided at 2510-2500 Ma. Then many other things were accreted until 1.8 Ga, as you mention, and we cite relevant papers, especially references 7-22, 25, 27, 28, 30, 35, and 67. The 1.8Ga topic is not the focus of this paper, and it has been addressed adequately in these other papers.
Line 60-63:'… causing deformation and metamorphism between 2.7-2.55 Ga to form protocontinental nucleii…'however, there are hardly metamorphism ages of 2.7-2.55 Ga in the North China craton. Actually, the widespread metamorphism in this craton was happened most likely after 2.55 Ga. BTW, 'nucleii' should read 'nuclei'?

REPLY:
That's not true, actually there are many reports on metamorphism around 2.7 -2.55 Ga 8,9,10 , which are overprinted by the strong 2.5 Ga collision events, then a second overprinting event around 1.85 Ga. Spelling mistake is corrected, thanks.
Line 72-80: the regional geology should start with the units defined by local workers, and then you may specify your tectonic interpretation for each unit. Based on what you define them as 'allochthonous' units? Ages different from the very small local basement? The tectonic contact among units? No strong speculation has been stated here or hereafter. The whole speculation is suspicious.

REPLY:
The allochthonous bodies/units in the Zanhuang region is reported in many previous works 6,7 , including in this journal. We think the reviewer is confused, thinking that we are reporting work from the unconformably overly 400-million-year younger undeformed basin sequence of the Gantaohe Group, which is, as stated, not allochthonous.
The allochthon is a forearc mélange complex, completely unrelated to the continental passive margin setting of our autochthonous sequence 7 . The tectonic contact between the allochthon the autochthon is a series of thrust faults 7,11 , with the closest fault to our sequence marked out in Fig. 7. The tectonic contact between the units within the sedimentary sequence is a major shear zone, very similar to the main nappe-bounding shear zones of the Alps 11 and Appalachians. The allochthonous nature of the overlying nappes is well-confirmed by numerous studies, based on solid field observation and mapping work, with good constraints from previous work on the arc-continent collision event and from our work on the pre-collisional sedimentation. Please see the publications cited above, including Zhong et al., 2021, and 2022, from this journal, and Geology.
Line 102-104: 'The quartz diorite … characteristic of mid-crust intrusions'. I do not aware that quartz diorite intrusives should be mid-crustal. Please show the observations and evidence.

REPLY:
Thank you for the question. The characteristic of mid-crust intrusions is that, under a higher temperature in the mid-crust, an unclear boundary and fuzzy contact is expected between the intrusion of small volume of magma body to the country rock, which matches to our field observation.
The evidence is shown in our detailed map, and photos, and data, in Figure 3, and in the related text. Considering that it is not essential to this work, related statement is deleted due to ambiguity.
Line 106-108: which episodes of deformation? Late Archaean or Paleoproterozoic (episodes as revealed by both zircon U-Pb and amphibole Ar-Ar ages)?
Paleoproterozoic. Without distinguishing the Archaean and Paleoproterozoic episodes of deformation, it is really hard to evaluate the description.
REPLY: Good point. However, Ar-Ar dating can be easily reset by thermal events because of its low closure temperature. The age of the deformation is determined by the crosscutting relationship, where ~2.50 Ga undeformed granitoid cut across the intensely deformed mélange, as reported in articles published in the past 10 years throughout the eastern margin of the COB. The overprinting metamorphism of the marble-metapelite unit is reported by 10 . Detailed constraints on tectonic events can be found in 6,7,11,12 .
Line 266-269: the error of these ages are quite large, over 20 Ma or 30 Ma. There are no obvious differences between these age groups to discriminate their provenances.

REPLY:
Right, the error can be 20 or 30 Ma. So, in our study we analysis >53 data for each sample, with careful observation and filtering to make sure the data are representing the magmatic formation age of each zircon. We interpret the provenance based on these sufficient data, among the high-quality data, using a variety of statistical methods that are well-established. The demonstration on the provenance discrimination methods can be referred to line 275-278. The differences of the ages in different samples can be referred to line 285-291. In the Supplementary Discussion 1, line 105-108, we have stated clearly that the data from detrital zircon is carefully filtered and properly interpretated to age calculation, and it is, therefore, valid in tectonic discrimination. This is described in great detail in the Supplementary Information, and represents the best age constraints, ever, on the autochthonous Archaean platform of the Zanhuang mélange belt. It is not the Gantaohe Group.
Line 270-286: I admit that there could be a successive thermal/igneous event in the region during the Late Archaean; then how can you distinguish ages between domains with lead loss and domains not, especially considering their large errors of singular ages.

REPLY:
Yes, you are right. Singular data with lead loss can be easily misinterpreted. That is the reason why we apply sufficient data to demonstrate the distribution pattern of the ages instead of using single zircons for interpretation. The diagram with distribution pattern is shown in Fig. 8, and the calculation methods to eliminate errors of single data are explained in detailed in the Supplementary Discussion 1, line 43-53. That is also why we also apply geological relationships of cross cutting Archaean dikes to show that the sequence is Archaean. The crosscutting relationship is described in main text, line 263-266 and shown in Fig. 2b, and its age constraints can be referred to lines 265-268, 330-346, and in the Supplementary data.
This confusion may be largely based on the reviewer believes we are dealing with the Proterozoic Gantaohe Group, which is much younger than the rock that we reported in this study.
Line 287-335: all these analyses and interpretation is based on the assumption that the sequence was the late Archaean in (depositional) age. But that was not the case, the volcanics (metabasalts) and other rocks show clear evidence that the rocks are middle Paleoproterozoic in age (e.g., Du et al., 2016;Liu et al., 2012).

REPLY:
Again, this confusion is based on the reviewer believes we are dealing with the Proterozoic Gantaohe Group. We are not.
Line 321-325: it analyzed the age of a crosscutting metamorphosed mafic dyke, which gives a U-Pb zircon age of 2507 Ma. I highly doubts whether this is an age of crystallization or an age from inherited zircon grains, and hence, it is inadequately proved that this ~2507 Ma age is a key to constrain the deposition age of the tectonostratigraphy.

REPLY:
We understand you doubts. It is apparently possible that mafic intrusion would have inherited zircon. That is why we have CL images provided in Supplementary Fig. 2e. In the figures we have shown the distinct differences between the inherited zircons (which have much older ages) and magmatic zircons. Please see the description in the supplementary data.
Line 338-340: But the whole basement was not exhumed until the Late Paleoproterozoic; how can it be the exposed coast in the Archaean.

REPLY:
The age issue has been addressed very clearly with multiple constrains, which can be referred to 'Geochronology constraints' section The statement that the Archaean basement exhumed in the late Paleoproterozoic in irrelevant to our work on the Archaean basement. The assumption of not being exhumed until the Paleoproterozoic is unsupportable. Again, this confusion is based on the reviewer believes we are dealing with the Proterozoic Gantaohe Group Lines 358-361: 'Thus, the results strongly suggest the autochthonous passive margin sequence was deposited concurrently with accretion of multiple arcs, with intervening oceans of different ages, in an accretionary orogen, similar in style to the Altaids of central Asia'. All the ages provided in the paper are within-error quite similar, and nothing of the kind can be supported.

REPLY:
We disagree. The arc accretionary setting is defined by regional tectonic studies and detrital zircon age distribution pattern, which is well explained in the text. We have ensured our data and interpretation meet with the quantity and quality, precision, and accuracy, which makes our statement valid. REPLY: An outburst is never an absolute terminology. The outburst in this scenario is relative to poor bioactivities in early Archaean. Our presumption is based of global data in Archaean biogenic carbonate platform, which is shown in Fig.10. The figure clearly supports our claim.
Reviewer #3 (Remarks to the Author): I would apologize for not being able to evaluate this revision in time. To avoid further delay, I would like to just focus the major concern of this manuscript -the age of the key units being stated in the paper. I would thank the authors to point out that these units were once mapped as the Fangjiapu Formation (this term was first used in 1961 but was abandoned later  2016)). I agree that more data are absolutely needed to give a better constrain (the whole units were metamorphosed), but please present evidence or better declaration if the authors think a part of this sequence is the Archean in age.   For naming issue, we abandoned the various old names assigned to these rocks, and their correlations with other units, as they were based on poor study on Archean orogenic events, resulting in the interpretation of the thrust sheets and nappes in an accretionary orogen (see for example the recent papers by 1,2 ) as a once continuous stratified sedimentary column stretching across tectonic units that were initially widely separated in space in time.
For the ages referred by reviewer 3, the poor quality and the inappropriate interpretation are the reason why we didn't refer to these works. The Zanhuang complex records a complex history of collision and accretion, and in such case, caution is needed in data interpretation. All the ages should be interpretated with integrated field relationships and accurate data analysis. Only when rigorous and systematic research is conducted, can the interpretation be reliable.
Our age is constrained by 290 valid detrital zircon ages with at least 53 for each, all with detailed description of field lithology and structural relationship. While the ages reported in those two papers are poor in quality, lack of field description, and thus are geological meaningless. Please see the attached "Letters to the Editor" published by Precambrian Research 3,4 , where we pointed out the sub-standard quality and quantity of data used both by SS Li et al (2016) 5 and L Tang et al (2016) 6 , which the authors of this group (led by M Santosh) keep propagating through the literature. Their interpretation also contracts the basic field relationships that we have established from years of detailed mapping in the Zanhuang massif 1,2,7,8,9 .
After the Archean history, that we focus on in this paper under consideration in Nature Communications, the region indeed experienced new widespread sedimentation and magmatism at about 2.1 Ga, which is well-described and analyzed in the recent papers by Peng Peng 10 and others.
Despite our clear disagreement about the age of these deformed strata, we thank Reviewer 3 for checking on thisone of the main driving forces for this research was to correct the idea that has wormed into the literature, from the papers by Tang 5 based on low-quality data, that these are simply Proterozoic, virtually undeformed strata. With our hundreds of new analyses, plus analyses of cross-cutting igneous rocks, we show that these rocks are clearly Archean, which has great implications for the start of the GOE, life, and how our planet has evolved, so as scientists, we insist on using high-quality data, before making models.

Attachment 1: Detailed response to the age issue
To help clear up the age dispute, we hereby plot together the sample locations of metasediments to which reviewer 3 refers, along with locations of other geochronological studies on the marble-metapelite unit, and our sequence, on Figure 1, our geological map. In this way, we compare all the data, and elaborate on the reasons why the age reviewer 3 suggested is incorrect.
[redacted] Figure 1. The sampling location in the article reviewer 3 refers to, another geochronological study on marble-metapelite unit , and our sequence.
Sample ZH-9 is a dolomite-calcite marble reported by  but has highly suspicious ages with huge analytical errors (figure 2), leading us (and Wang et al., 2017a) to conclude that the data and conclusion based upon that data are untenable. The authors only present 13 data points (excluding many more), which is not enough to rule out contamination and anomalous data, and very far from enough for a statistically valid detrital zircon study. In our study, we present 290 analyses, sufficient for a robust statistical analysis. Furthermore, the CL images of this sample (figure 7d in the original article) show significant hydrothermal alteration (Figure 3; outlined by a while solid line), which overlaps with their analytical spots (yellow circles), showing that their younger age result is clearly a result of contamination, and has no meaning as a depositional age constraint.
This was the subject of the "Letter to the Editor" by JP  stating that the data presented by L Tang et al was low quality and meaningless. The Letter is attached. [redacted] Figure  4), comes from sample Z54-1. The ages from this sample are highly discordant, which is unqualified to use as a constraint to estimate depositional age. Moreover, no field observations or descriptions of the lithology of this specific sample are reported in the original article to support their notion, and the way they illustrate structural relationships is rough and unclear (figure 5, left) compared to the more accurate ones of all the detailed structures and lithologies from our studies (Figure 5 right). In contrast, another study carried